Particularly in the case of shavers having one or more (rechargeable) batteries as the power source, it is important to minimize the friction between cooperating parts and hence the mechanical losses.
An important source of mechanical losses is the friction between the cooperating parts of the shaving unit.
The shaving units of shavers become soiled relatively rapidly during operation. The parts of the shaving unit contact facial hairs, scales, perspiration and sebaceous matter. Substances present on the skin such as water, residues of soap or cosmetic products, dust and the like also contribute to the soiling of the shaving units.
As a consequence, the number of shaves which can be performed, for example, with one charge in the case of battery-powered shavers decreases in time, and in all types of shavers the efficiency of the shaving unit may also descrease.
In European Patent Specification 0 087 836, which corresponds substantially to U.S. Pat. No. 4,525,417, issued Jun. 25, 1985, a description is given of a friction-reducing layer which comprises carbon and a metal, the atomic ratio between carbon and metal ranging between 50.1/49.9 and 99.9/0.1 and the ratio of metal to carbon differing from the stoichiometric ratio of a carbide. Preferably, this ratio ranges between 60/40 and 97/3, the best results being obtained at ratios between 80/20 and 95/5. Besides carbon and metal the layer may comprise impurities that results from the atmosphere from which the layers are deposited. In practice it has been found that such an impurity consists of, for example, hydrogen, if a hydrocarbon atmosphere has been used to deposit the carbon. The layers are generally X-ray amorphous and do not have the stoichiometric composition of a carbide.
In the said European Patent Specification 00 87 836 it is stated that the friction-reducing layers can be applied to, amongst others, shaving heads of electric shavers. It is stated that the lowest coefficient of friction is obtained if both cooperating faces are covered with the friction-reducing layer.
We have found that the operating conditions of shavers having a rotating cutting member are such that if both parts are covered with a friction-reducing metal-carbon layer the coefficient of friction between the cooperating parts of the shaving unit is higher when in the case that only one of the parts is covered with such a friction-reducing layer. Moreover, it has been found that preferably only the shear plate should be covered with such a layer.